Sprockets incorporating metal cushion rings have been used in automotive engine roller chain drive systems such as camshaft and balance shaft drives. The purpose of the cushion rings is to buffer or soften the roller-sprocket collision at the onset of meshing, thereby acting to reduce the chain meshing noise levels associated with roller chain drive systems. Roller-sprocket impact at the onset of meshing is the dominant noise source associated with roller chain drive systems and it occurs when a chain link leaves the span and its meshing roller collides with the sprocket tooth at engagement. It is believed that multiple roller-sprocket tooth impacts occur during the meshing phenomena and these impacts contribute to the undesirable noise levels associated with roller chain drives.
FIGS. 1 and 2 illustrate a conventional sprocket assembly S including a sprocket body 10, circular metal cushion rings 12a, 12b positioned respectively adjacent first and second axial faces 14a, 14b of a sprocket body 10. The sprocket body 10 defines a bore B or other recess about a central axis of rotation L, and first and second hubs 16a, 16b project axially outward in opposite directions from the first and second faces 14a, 14b, respectively. The hubs 16a, 16b each define a cylindrical outer diameter that is centered on the axis L and that is received within the inner diameter of each of the rings 12a,12b. The inner diameter of the rings 12a, 12b is larger than the outer diameter of the hubs 16a, 16b so that the rings 12a, 12b are able to float eccentrically thereon.
First and second retaining devices such as retaining rings/clips 18a, 18b are seated in grooves 19a, 19b of the hubs 16a, 16b and capture the first and second rings 12a, 12b on the first and second hubs, while still allowing the eccentric floating movement of the rings 12a, 12b on the outer diameter of the hubs. Other retaining devices or means for retaining/capturing the first and second rings 12a, 12b on the hubs can be used, e.g., welded plates or other clipping arrangements can be attached to the first and second hubs to capture the first and second rings, respectively.
The sprocket body 10 further comprises a plurality of teeth 20 defined therein and separated from each other by tooth spaces 22. Each tooth 20 includes an “engaging” or “drive” flank 24 and a “disengaging” or “coast” flank 26, with the drive flank 24 being downstream relative to the coast flank 26 in terms of the direction in which the sprocket rotates (see arrow 11). As such, the tooth spaces 22 are defined between circumferentially successive drive and coast flanks 24,26. The teeth 20 (and tooth spaces 22) can be either symmetrical or asymmetrical.
The sprocket body 10 is defined from any suitable material such as one-piece construction by compacted powdered metal techniques, or machined from steel, or the like. The rings 12a, 12b are typically defined from a suitable metal such as bearing-grade steel.
As is well known, the link plates of an associated chain, e.g., a roller chain or bush chain, will come into contact with the outside diameter of the cushion rings 12a, 12b prior to chain-sprocket meshing, and this contact serves to control and dampen transverse vibration in the chain span, and thereby buffer or soften roller-sprocket impact during the meshing phenomenon. As the chain link plates come into contact with and lay on the outer surface of the rings 12a, 12b during the onset of meshing, the rings 12a, 12b gradually move to a position and/or deform to a shape that allows the chain rollers to mesh fully with the sprocket teeth 20 in the tooth spaces 22. Sprocket assemblies S as described are typically used in automotive chain drive systems such as timing and/or balance shaft drive systems.